Dentifrice Formulations Having Spherical Stannous Compatible Silica Particles for Reduced RDA

ABSTRACT

Dentifrice containing silica particles having a d50 median particle size from 4 to 25 μm, a BET surface area of less than 10 m2/g, and a total mercury intrusion pore volume from 0.2 to 1.5 cc/g, are disclosed.

BACKGROUND OF THE INVENTION

Compositions containing stannous, including stannous fluoride, are usedin toothpaste and other dentifrice applications, providing improvedcavity protection and reduced plaque, gingivitis, and tooth sensitivity.However, the effectiveness of stannous in a dentifrice composition canbe diminished due to interactions with other components of theformulation, such as silica materials. Therefore, it would be beneficialto provide silica materials with improved stannous compatibility toimprove the overall effectiveness of the stannous in a dentifricecomposition.

Relative dentin abrasion (RDA) is a test that is used to set safetylimits for toothpaste and other dentifrice compositions. The RDA testinvolves measuring the loss of dentin after brushing with a testtoothpaste formulation relative to the control calcium pyrophosphate(set to 100). Spherical silica particles, as compared to traditionalnon-spherical and irregularly shaped silica particles, have certainproperties (such as low Einlehner abrasion) that are beneficial fortheir use in toothpaste and other dentifrice applications. However, itwould be advantageous for these spherical silica materials also to haveimproved RDA performance.

Therefore, the present invention is principally directed to a dentifricecomprising spherical silica particles having a beneficial combination ofboth improved stannous compatibility and improved RDA performance.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the detaileddescription. This summary is not intended to identify required oressential features of the claimed subject matter. Nor is this summaryintended to be used to limit the scope of the claimed subject matter.

Dentifrice having silica particles with reduced Relative Dentin Abrasion(RDA) and increased stannous compatibility are disclosed and describedherein.

A dentifrice composition is provided that comprises binder; surfactant;silica particles; wherein the silica particles comprise a d50 medianparticle size in a range from about 4 to about 25 μm; a BET surface areain a range from 0 to about 10 m²/g; and a total mercury intrusion porevolume in a range from about 0.2 to about 1.5 cc/g.

In accordance with an aspect of this invention, such silica particlescan have (i) a d50 median particle size in a range from about 4 to about25 μm (or from about 6 to about 25 μm, or from about 8 to about 20 μm),(ii) a sphericity factor (S₈₀) of greater than or equal to about 0.9 (orgreater than or equal to about 0.92), (iii) a BET surface area in arange from 0 to about 10 m²/g (or from about 0.05 to about 8 m²/g), and(iv) a total mercury intrusion pore volume in a range from about 0.35 toabout 1.1 cc/g (or from about 0.35 to about 0.7 cc/g, or from about 0.4to about 0.65 cc/g). These silica particles have a spherical shape ormorphology, and can be produced using a continuous loop reactor process.

Both the foregoing summary and the following detailed descriptionprovide examples and are explanatory only. Accordingly, the foregoingsummary and the following detailed description should not be consideredto be restrictive. Further, features or variations may be provided inaddition to those set forth herein. For example, certain aspects may bedirected to various feature combinations and sub-combinations describedin the detailed description.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of the continuous loop reactor apparatus used toproduce the silica products of Examples 2A-6A.

FIG. 2 is Scanning Electron Micrographs of the silica of Example 2A.

FIG. 3 is Scanning Electron Micrographs of the silica of Example 3A.

FIG. 4 is Scanning Electron Micrographs of the silica of Example 4A.

FIG. 5 is Scanning Electron Micrographs of the silica of Example 5A.

FIG. 6 is Scanning Electron Micrographs of the silica of Example 6A.

FIG. 7 is a model for a 4 μm spherical particle interacting with a 2.5μm dentin tubule.

FIG. 8 is a model for spherical particles of increasing particle size (4μm, 5 μm, 6 μm, 10 μm) interacting with dentin tubules of 2.5 μm.

FIG. 9 is a plot of the depth of penetration, in a 2.5 μm width dentintubule, versus particle diameter for a sphere.

FIG. 10 is a plot of the force required to roll a sphere out of a 2.5 μmwidth tubule as a function of increasing particle diameter for a sphere.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed herein are dentifrices having generally spherical silicaparticles that can be characterized by (i) a d50 median particle size ina range from about 4 to about 25 μm (or from about 6 to about 25 μm, orfrom about 8 to about 20 μm), (ii) a sphericity factor (S₈₀) of greaterthan or equal to about 0.9 (or greater than or equal to about 0.92),(iii) a BET surface area in a range from 0 to about 10 m²/g (or fromabout 0.05 to about 8 m²/g), and (iv) a total mercury intrusion porevolume in a range from about 0.35 to about 1.1 cc/g (or from about 0.35to about 0.7 cc/g, or from about 0.4 to about 0.65 cc/g). Methods ofmaking these spherical silica particles, and dentifrice compositionscontaining the spherical particles, also are disclosed and describedherein.

Beneficially, the spherical particles disclosed and described hereinhave an unexpected combination of low RDA and high stannouscompatibility.

To define more clearly the terms used herein, the following definitionsare provided. Unless otherwise indicated, the following definitions areapplicable to this disclosure. If a term is used in this disclosure butis not specifically defined herein, the definition from the IUPACCompendium of Chemical Terminology, 2nd Ed (1997), can be applied, aslong as that definition does not conflict with any other disclosure ordefinition applied herein, or render indefinite or non-enabled any claimto which that definition is applied. To the extent that any definitionor usage provided by any document incorporated herein by referenceconflicts with the definition or usage provided herein, the definitionor usage provided herein controls.

Herein, features of the subject matter are described such that, withinparticular aspects, a combination of different features can beenvisioned. For each and every aspect and each and every featuredisclosed herein, all combinations that do not detrimentally affect thedesigns, compositions, processes, or methods described herein arecontemplated and can be interchanged, with or without explicitdescription of the particular combination. Accordingly, unlessexplicitly recited otherwise, any aspect or feature disclosed herein canbe combined to describe inventive designs, compositions, processes, ormethods consistent with the present disclosure.

By “oral care composition”, as used herein, is meant a product, which inthe ordinary course of usage, is not intentionally swallowed forpurposes of systemic administration of particular therapeutic agents,but is rather retained in the oral cavity for a time sufficient tocontact dental surfaces or oral tissues. Examples of oral carecompositions include dentifrice, tooth gel, subgingival gel, mouthrinse, mousse, foam, mouth spray, lozenge, chewable tablet, chewing gum,tooth whitening strips, floss and floss coatings, breath fresheningdissolvable strips, or denture care or adhesive product. The oral carecomposition may also be incorporated onto strips or films for directapplication or attachment to oral surfaces.

The term “dentifrice”, as used herein, includes tooth orsubgingival—paste, gel, or liquid formulations unless otherwisespecified. The dentifrice composition may be a single phase compositionor may be a combination of two or more separate dentifrice compositions.The dentifrice composition may be in any desired form, such as deepstriped, surface striped, multilayered, having a gel surrounding apaste, or any combination thereof. Each dentifrice composition in adentifrice comprising two or more separate dentifrice compositions maybe contained in a physically separated compartment of a dispenser anddispensed side-by-side.

“Active and other ingredients” useful herein may be categorized ordescribed herein by their cosmetic and/or therapeutic benefit or theirpostulated mode of action or function. However, it is to be understoodthat the active and other ingredients useful herein can, in someinstances, provide more than one cosmetic and/or therapeutic benefit orfunction or operate via more than one mode of action. Therefore,classifications herein are made for the sake of convenience and are notintended to limit an ingredient to the particularly stated function(s)or activities listed.

The term “teeth”, as used herein, refers to natural teeth as well asartificial teeth or dental prosthesis and is construed to comprise onetooth or multiple teeth. The term “tooth surface” as used herein, refersto natural tooth surface(s) as well as artificial tooth surface(s) ordental prosthesis surface(s) accordingly.

While compositions and methods are described herein in terms of“comprising” various components or steps, the compositions and methodscan also “consist essentially of” or “consist of” the various componentsor steps, unless stated otherwise.

As used herein, the word “or” when used as a connector of two or moreelements is meant to include the elements individually and incombination; for example X or Y, means X or Y or both.

As used herein, the articles “a” and “an” are understood to mean one ormore of the material that is claimed or described, for example, “an oralcare composition” or “a bleaching agent.”

All measurements referred to herein are made at about 23° C. (i.e. roomtemperature) unless otherwise specified.

Generally, groups of elements are indicated using the numbering schemeindicated in the version of the periodic table of elements published inChemical and Engineering News, 63(5), 27, 1985. In some instances, agroup of elements can be indicated using a common name assigned to thegroup; for example, alkali metals for Group 1 elements, alkaline earthmetals for Group 2 elements, and so forth.

Although any methods and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of theinvention, the typical methods and materials are herein described.

All publications and patents mentioned herein are incorporated herein byreference for the purpose of describing and disclosing, for example, theconstructs and methodologies that are described in the publications,which might be used in connection with the presently describedinvention.

Several types of ranges are disclosed in the present invention. When arange of any type is disclosed or claimed, the intent is to disclose orclaim individually each possible number that such a range couldreasonably encompass, including end points of the range as well as anysub-ranges and combinations of sub-ranges encompassed therein. As arepresentative example, the BET surface area of the silica particles canbe in certain ranges in various aspects of this invention. By adisclosure that the BET surface area is in a range from 0 to about 10m²/g, the intent is to recite that the surface area can be any surfacearea within the range and, for example, can be equal to about 0.1, about0.5, about 1, about 2, about 3, about 4, about 5, about 6, about 7,about 8, about 9, or about 10 m²/g. Additionally, the surface area canbe within any range from 0 to about 10 m²/g (for example, from about0.05 to about 8 m²/g), and this also includes any combination of rangesbetween 0 and about 10 m²/g (for example, the surface area can be in arange from about 0.1 to about 3, or from about 5 to about 7 m²/g).Likewise, all other ranges disclosed herein should be interpreted in amanner similar to this example.

The term “about” means that amounts, sizes, formulations, parameters,and other quantities and characteristics are not and need not be exact,but can be approximate and/or larger or smaller, as desired, reflectingtolerances, conversion factors, rounding off, measurement errors, andthe like, and other factors known to those of skill in the art. Ingeneral, an amount, size, formulation, parameter or other quantity orcharacteristic is “about” or “approximate” whether or not expresslystated to be such. The term “about” also encompasses amounts that differdue to different equilibrium conditions for a composition resulting froma particular initial mixture. Whether or not modified by the term“about,” the claims include equivalents to the quantities. The term“about” can mean within 10% of the reported numerical value, preferablywithin 5% of the reported numerical value.

Spherical Silica Particles

An illustrative and non-limiting example of silica particles consistentwith the present invention can have the following characteristics: (i) ad50 median particle size in a range from about 4 to about 25 μm, (ii) asphericity factor (S₈₀) of greater than or equal to about 0.9, (iii) aBET surface area in a range from 0 to about 10 m²/g, and (iv) a totalmercury intrusion pore volume in a range from about 0.2 to about 1.5cc/g. Another illustrative and non-limiting example of silica particlesconsistent with the present invention can have the followingcharacteristics: (i) a d50 median particle size in a range from about 6to about 25 μm, (ii) a sphericity factor (S₈₀) of greater than or equalto about 0.9, (iii) a BET surface area in a range from 0 to about 8m²/g, and (iv) a total mercury intrusion pore volume in a range fromabout 0.35 to about 1.1 cc/g. Yet another illustrative and non-limitingexample of silica particles consistent with the present invention canhave the following characteristics: (i) a d50 median particle size in arange from about 8 to about 20 μm, (ii) a sphericity factor (S₈₀) ofgreater than or equal to about 0.9, (iii) a BET surface area in a rangefrom 0 to about 8 m²/g, and (iv) a total mercury intrusion pore volumein a range from about 0.35 to about 0.7 cc/g. In further aspects, suchsilica particles consistent with the present invention also can have anyof the characteristics or properties provided below, and in anycombination.

In an aspect, the spherical silica particles can have a relatively largeaverage particle size. Often, the median particle size (d50) and/or meanparticle size (average) can fall within a range from about 4 to about25, from about 4 to about 20, from about 6 to about 25, from about 6 toabout 22, from about 6 to about 18, from about 7 to about 25, from about7 to about 20, or from about 7 to about 18 μm, and the like. In anotheraspect, the median particle size (d50) and/or mean particle size(average) can fall within a range from about 8 to about 25, from about 8to about 20, from about 8 to about 18, from about 8 to about 15, fromabout 9 to about 16, or from about 9 to about 14 μm. Other appropriateranges for the mean and median particle sizes are readily apparent fromthis disclosure.

The spherical particles also have a very narrow particle sizedistribution, which can be quantified by the ratio of (d90-d10)/d50. Alower value for the ratio indicates a narrower particle sizedistribution, while a larger value for the ratio indicates a broaderparticle size distribution. Generally, the spherical particles disclosedherein can be characterized by a ratio of (d90-d10)/d50 in a range fromabout 1.1 to about 2.4. In one aspect, the ratio of (d90-d10)/d50 can bein a range from about 1.1 to about 2.2, while in another aspect, theratio of (d90-d10)/d50 can be in a range from about 1.1 to about 2, fromabout 1.1 to about 1.7, or from about 1.3 to about 1.5. Yet, in anotheraspect, the ratio of (d90-d10)/d50 can be in a range from about 1.2 toabout 2.4, while in still another aspect, the ratio of (d90-d10)/d50 canbe in a range from about 1.2 to about 2.2, or from about 1.2 to about 2.Other appropriate ranges for the ratio of (d90-d10)/d50 are readilyapparent from this disclosure.

Another indicator of the narrow particle size distribution of thespherical silica particles is the weight percentage of 325 mesh residue(amount retained in a 325 mesh sieve), which can be less than or equalto about 1.2 wt. %. In some aspects, the 325 mesh residue can be lessthan or equal to about 1 wt. %, less than or equal to about 0.75 wt. %,less than or equal to about 0.6 wt. %, or less than or equal to about0.3 wt. %. Other appropriate ranges for the 325 mesh residue are readilyapparent from this disclosure.

Sphericity of the spherical silica particles can be quantified by asphericity factor (S₈₀), which can be greater than or equal to about0.85, greater than or equal to about 0.88, or greater than or equal toabout 0.9. The sphericity factor (S₈₀) is determined as follows. An SEMimage of the silica particle sample is magnified 20,000 times, which isrepresentative of the silica particle sample, and is imported into photoimaging software, and the outline of each particle (two-dimensionally)is traced. Particles that are close in proximity to one another but notattached to one another should be considered separate particles for thisanalysis. The outlined particles are then filled in with color, and theimage is imported into particle characterization software (e.g.,IMAGE-PRO PLUS available from Media Cybernetics, Inc., Bethesda, Md.)capable of determining the perimeter and area of the particles.Sphericity of the particles can then be calculated according to theequation, Sphericity=(perimeter)² divided by (4π×area), whereinperimeter is the software measured perimeter derived from the outlinedtrace of the particles, and wherein area is the software measured areawithin the traced perimeter of the particles.

The sphericity calculation is performed for each particle that fitsentirely within the SEM image. These values are then sorted by value,and the lowest 20% of these values are discarded. The remaining 80% ofthese values are averaged to obtain the sphericity factor (S₈₀).Additional information on sphericity can be found in U.S. Pat. Nos.8,945,517 and 8,609,068, incorporated herein by reference in theirentirety.

In one aspect of this invention, the spherical silica particles can havea sphericity factor (S₈₀) greater than or equal to about 0.85, orgreater than or equal to about 0.88, while in another aspect, thesphericity factor (S₈₀) can be greater than or equal to about 0.9. Yet,in another aspect, the spherical silica particles can be characterizedby a sphericity factor (S₈₀) greater than or equal to about 0.92, and instill another aspect, the silica particles can be characterized by asphericity factor (S₈₀) greater than or equal to about 0.94. As one ofskill in the art would readily recognize, a 3-dimensional sphere (or2-dimensional circle) will have a sphericity factor (S₈₀) equal to 1.

In an aspect, the silica particles can have a very low surface area,generally a BET surface area ranging from 0 to about 10 m²/g. Often, theBET surface area can fall within a range from about 0.05 to about 10,from about 0.1 to about 10, from about 0.25 to about 10, or from about0.05 to about 8 m²/g. In further aspects, the BET surface area can be ina range from about 0.25 to about 8, from about 0.5 to about 8, fromabout 0.1 to about 5, from about 0.25 to about 5, from about 0.5 toabout 5, from about 0.25 to about 3.5, or from about 0.5 to about 2m²/g, and the like. The BET surface area also can fall within a rangefrom 0 to about 8 m²/g, from 0 to about 5 m²/g, or from 0 to about 3m²/g. Other appropriate ranges for the BET surface area are readilyapparent from this disclosure.

Likewise, the total mercury intrusion pore volume of the silicaparticles is also relatively low, often falling within a range fromabout 0.2 to about 1.5, from about 0.3 to about 1.1, from about 0.35 toabout 1.1, from about 0.35 to about 0.7, from about 0.35 to about 0.65,from about 0.35 to about 0.62, or from about 0.35 to about 0.6 cc/g. Inanother aspect, the total mercury intrusion pore volume of the silicaparticles can be from about 0.4 to about 0.7 cc/g, from about 0.4 toabout 0.65 cc/g, from about 0.45 to about 0.65 cc/g, or from about 0.49to about 0.6 cc/g. Other appropriate ranges for the total mercuryintrusion pore volume are readily apparent from this disclosure.

Additionally, the spherical silica particles can be less abrasive, asreflected by an Einlehner abrasion value ranging from about 7 to about25 mg lost/100,000 revolutions. For instance, the Einlehner abrasionvalue can be in a range from about 8 to about 20; alternatively, fromabout 10 to about 20; or alternatively, from about 15 to about 22 mglost/100,000 revolutions. The Einlehner abrasion value also can be in arange from about 10 to about 25 mg lost/100,000 revolutions, from about10 to about 22 mg lost/100,000 revolutions, or from about 11 to about 17mg lost/100,000 revolutions. Other appropriate ranges for the Einlehnerabrasion value are readily apparent from this disclosure.

Likewise, these spherical silica particles also have a relatively highpour density. In one aspect, the pour density can be in a range fromabout 30 to about 65 lb/ft³, or from about 40 to about 65 lb/ft³. Inanother aspect, the pour density can be in a range from about 40 toabout 62 lb/ft³, from about 42 to about 60 lb/ft³, or from about 43 toabout 58 lb/ft³. In yet another aspect, the pour density can be in therange from about 42 to about 56 lb/ft³, or from about 44 to about 54lb/ft³. Other appropriate ranges for the pour density are readilyapparent from this disclosure.

Spherical silica particles in accordance with aspects of this inventioncan have excellent stannous compatibility and excellent CPCcompatibility. Typically, the spherical silica particles describedherein have a stannous compatibility from about 40 to about 99%, suchas, for instance, from about 80 to about 99%, from about 75 to about98%, from about 75 to about 95%, from about 80 to about 95%, from about82 to about 98%, or from about 86 to about 93%, and the like.Additionally, the spherical silica particles typically have a CPCcompatibility from about 55 to about 99%, such as, for instance, fromabout 40 to about 95%, from about 75 to about 95%, from about 78 toabout 95%, or from about 81 to about 91%, and the like. Otherappropriate ranges for the stannous compatibility and CPC compatibilityare readily apparent from this disclosure.

In another aspect, the spherical silica particles can have relativelylow oil absorption, relatively low water absorption, and very low CTABsurface area. For instance, the oil absorption can be in a range fromabout 20 to about 75 cc/100 g, from about 25 to about 60 cc/100 g, fromabout 25 to about 55 cc/100 g, or from about 32 to about 50 cc/100 g.Additionally or alternatively, the water absorption can be in a rangefrom about 40 to about 75 cc/100 g, from about 45 to about 72 cc/100 g,from about 50 to about 70 cc/100 g, from about 50 to about 65 cc/100 g,or from about 57 to about 66 cc/100 g. Representative and non-limitingranges for the CTAB surface include from 0 to about 10 m²/g, from 0 toabout 6 m²/g, from 0 to about 4 m²/g, or from 0 to about 2 m²/g. Otherappropriate ranges for the oil absorption, the water absorption, and theCTAB surface area are readily apparent from this disclosure.

While not limited thereto, the disclosed spherical silica particles canhave a loss on drying (LOD) that often falls within a range from about 1to about 10 wt. %. Illustrative and non-limiting ranges for the LODinclude from about 1 to about 8 wt. %, from about 2 to about 8 wt. %,from about 1 to about 7 wt. %, from about 1 to about 5 wt. %, from about1 to about 4 wt. %, or from about 1.5 to about 2 wt. %. Likewise, whilenot limited thereto, the disclosed spherical silica particles can have aloss on ignition (LOI) that often falls within a range from about 3 toabout 10 wt. %. Illustrative and non-limiting ranges for the LOI includefrom about 3 to about 8 wt. %, from about 3 to about 7 wt. %, from about3 to about 6 wt. %, from about 3.5 to about 9 wt. %, from about 3.5 toabout 7.5 wt. %, or from about 3.5 to about 6 wt. %. Other appropriateranges for the LOD and LOI are readily apparent from this disclosure.

Generally, the spherical silica particles can have a substantiallyneutral pH that encompasses, for instance, a pH range of from about 5.5to about 9, from about 6.2 to about 8.5, or from about 6.8 to about 8.2.Other appropriate ranges for the pH are readily apparent from thisdisclosure.

The Relative Dentin Abrasion (RDA) test is typically performed toconfirm that a dentifrice composition, e.g., toothpaste, is safe forconsumer use, with the upper limit of the test set at 250. Unexpectedly,the results provided herein demonstrate that, for the spherical silicaparticles consistent with this invention, the RDA generally decreases asthe median particle size (d50) and/or mean particle size (average)increases. The spherical silica particles can be characterized by a RDAat 20 wt. % loading of less than about 250, or in a range from about 100to about 220, in one aspect of this invention, and from about 120 toabout 200 in another aspect. Other illustrative and non-limiting rangesfor the RDA at 20 wt. % loading can include from about 50 to about 200,from about 80 to about 200, from about 80 to about 150, from about 130to about 190, from about 130 to about 180, from about 150 to about 200,from about 150 to about 190, or from about 168 to about 182. Otherappropriate ranges for the RDA are readily apparent from thisdisclosure.

The spherical silica particles also can be described by their PellicleCleaning Ratio (PCR), which is a measure of the cleaning characteristicsof a dentifrice composition containing the silica particles. The silicaparticles can be characterized by a PCR at 20 wt. % loading in a rangeabout 70 to about 130, from about 80 to about 130, from about 70 toabout 120, from about 80 to about 120, or from about 90 to about 110.The PCR/RDA ratio (at 20 wt. % loading) often can be from about 0.4:1 toabout 1.1:1, from about 0.4:1 to about 0.8:1, from about 0.5:1 to about1:1, from about 0.5:1 to about 0.7:1, from about 0.45:1 to about 0.65:1,or from about 0.56:1 to about 0.57:1.

In these and other aspects, any of the spherical silica particles can beamorphous, can be synthetic, or can be both amorphous and synthetic.Moreover, the spherical silica particles can comprise (or consistessentially of, or consist of) precipitated silica particles inparticular aspects of this invention, although not limited thereto.

Dentifrice Compositions

The spherical silica particles can be used in any suitable compositionand for any suitable end-use application. Often, the silica particlescan be used in oral care applications, such as in a dentifricecomposition. The dentifrice composition can contain any suitable amountof the silica particles, such as from about 0.5 to about 50 wt. %, fromabout 1 to about 50 wt. %, from about 5 to about 35 wt. %, from about 10to about 40 wt. %, or from about 10 to about 30 wt. %, of the sphericalsilica particles. These weight percentages are based on the total weightof the dentifrice composition.

The dentifrice composition can be in any suitable form, such as a solid,liquid, powder, paste, or combinations thereof. In addition to thesilica particles, the dentifrice composition can contain otheringredients or additives, non-limiting examples of which can include ahumectant, a solvent, a binder, a therapeutic agent, a chelating agent,a thickener other than the silica particles, a surfactant, an abrasiveother than the silica particles, a sweetening agent, a colorant, aflavoring agent, a preservative, and the like, as well as anycombination thereof.

Humectants serve to add body or “mouth texture” to a dentifrice as wellas preventing the dentifrice from drying out. Suitable humectantsinclude polyethylene glycol (at a variety of different molecularweights), propylene glycol, glycerin (glycerol), erythritol, xylitol,sorbitol, mannitol, lactitol, and hydrogenated starch hydrolyzates, andmixtures thereof. In some formulations, humectants are present in anamount from about 20 to about 50 wt. %, based on the weight of thedentifrice composition.

A solvent can be present in the dentifrice composition, at any suitableloading, and usually the solvent comprises water. When used, water ispreferably deionized and free of impurities, can be present in thedentifrice at loadings from 5 to about 70 wt. %, or from about 5 toabout 35 wt. %, based on the weight of dentifrice composition.

Therapeutic agents also can be used in the compositions of thisinvention to provide for the prevention and treatment of dental caries,periodontal disease, and temperature sensitivity, for example. Suitabletherapeutic agents can include, but are not limited to, fluoridesources, such as sodium fluoride, sodium monofluorophosphate, potassiummonofluorophosphate, stannous fluoride, potassium fluoride, sodiumfluorosilicate, ammonium fluorosilicate and the like; condensedphosphates such as tetrasodium pyrophosphate, tetrapotassiumpyrophosphate, disodium dihydrogen pyrophosphate, trisodium monohydrogenpyrophosphate; tripolyphosphates, hexametaphosphates, trimetaphosphatesand pyrophosphates; antimicrobial agents such as triclosan, bisguanides,such as alexidine, chlorhexidine and chlorhexidine gluconate; enzymessuch as papain, bromelain, glucoamylase, amylase, dextranase, mutanase,lipases, pectinase, tannase, and proteases; quaternary ammoniumcompounds, such as benzalkonium chloride (BZK), benzethonium chloride(BZT), cetylpyridinium chloride (CPC), and domiphen bromide; metalsalts, such as zinc citrate, zinc chloride, and stannous fluoride;sanguinaria extract and sanguinarine; volatile oils, such as eucalyptol,menthol, thymol, and methyl salicylate; amine fluorides; peroxides andthe like. Therapeutic agents can be used in dentifrice formulationssingly or in combination, and at any therapeutically safe and effectivelevel or dosage.

Thickening agents are useful in the dentifrice compositions to provide agelatinous structure that stabilizes the toothpaste against phaseseparation. Suitable thickening agents include silica thickener; starch;glycerite of starch; gums such as gum karaya (sterculia gum), gumtragacanth, gum arabic, gum ghatti, gum acacia, xanthan gum, guar gumand cellulose gum; magnesium aluminum silicate (Veegum); carrageenan;sodium alginate; agar-agar; pectin; gelatin; cellulose compounds such ascellulose, carboxymethyl cellulose, hydroxyethyl cellulose,hydroxypropyl cellulose, hydroxymethyl cellulose, hydroxymethylcarboxypropyl cellulose, methyl cellulose, ethyl cellulose, and sulfatedcellulose; natural and synthetic clays such as hectorite clays; andmixtures thereof. Typical levels of thickening agents or binders are upto about 15 wt. % of a toothpaste or dentifrice composition.

Useful silica thickeners for utilization within a toothpastecomposition, for example, include, as a non-limiting example, anamorphous precipitated silica such as ZEODENT® 165 silica. Othernon-limiting silica thickeners include ZEODENT® 153, 163, and 167, andZEOFREE® 177 and 265 silica products, all available from EvonikCorporation, and AEROSIL® fumed silicas.

Surfactants can be used in the dentifrice compositions of the inventionto make the compositions more cosmetically acceptable. The surfactant ispreferably a detersive material which imparts to the compositiondetersive and foaming properties. Suitable surfactants are safe andeffective amounts of anionic, cationic, nonionic, zwitterionic,amphoteric and betaine surfactants, such as sodium lauryl sulfate,sodium dodecyl benzene sulfonate, alkali metal or ammonium salts oflauroyl sarcosinate, myristoyl sarcosinate, palmitoyl sarcosinate,stearoyl sarcosinate and oleoyl sarcosinate, polyoxyethylene sorbitanmonostearate, isostearate and laurate, sodium lauryl sulfoacetate,N-lauroyl sarcosine, the sodium, potassium, and ethanolamine salts ofN-lauroyl, N-myristoyl, or N-palmitoyl sarcosine, polyethylene oxidecondensates of alkyl phenols, cocoamidopropyl betaine, lauramidopropylbetaine, palmityl betaine and the like. Sodium lauryl sulfate is apreferred surfactant. The surfactant is typically present in thecompositions of the present invention in an amount from about 0.1 toabout 15 wt. %, from about 0.3 to about 5 wt. %, or from about 0.3 toabout 2.5 wt. %.

The disclosed silica particles can be utilized alone as the abrasive inthe dentifrice composition, or as an additive or co-abrasive with otherabrasive materials discussed herein or known in the art. Thus, anynumber of other conventional types of abrasive additives can be presentwithin the dentifrice compositions of the invention. Other such abrasiveparticles include, for example, precipitated calcium carbonate (PCC),ground calcium carbonate (GCC), chalk, bentonite, dicalcium phosphate orits dihydrate forms, silica gel (by itself, and of any structure),precipitated silica, amorphous precipitated silica (by itself, and ofany structure as well), perlite, titanium dioxide, dicalcium phosphate,calcium pyrophosphate, alumina, hydrated alumina, calcined alumina,aluminum silicate, insoluble sodium metaphosphate, insoluble potassiummetaphosphate, insoluble magnesium carbonate, zirconium silicate,particulate thermosetting resins and other suitable abrasive materials.Such materials can be introduced into the dentifrice compositions totailor the polishing characteristics of the target formulation.

Sweeteners can be added to the dentifrice composition (e.g., toothpaste)to impart a pleasing taste to the product. Suitable sweeteners includesaccharin (as sodium, potassium or calcium saccharin), cyclamate (as asodium, potassium or calcium salt), acesulfame-K, thaumatin,neohesperidin dihydrochalcone, ammoniated glycyrrhizin, dextrose,levulose, sucrose, mannose, and glucose.

Colorants can be added to improve the aesthetic appearance of theproduct. Suitable colorants include without limitation those colorantsapproved by appropriate regulatory bodies such as the FDA and thoselisted in the European Food and Pharmaceutical Directives and includepigments, such as TiO₂, and colors such as FD&C and D&C dyes.

Flavoring agents also can be added to dentifrice compositions. Suitableflavoring agents include, but are not limited to, oil of wintergreen,oil of peppermint, oil of spearmint, oil of sassafras, and oil of clove,cinnamon, anethole, menthol, thymol, eugenol, eucalyptol, lemon, orangeand other such flavor compounds to add fruit notes, spice notes, etc.These flavoring agents generally comprise mixtures of aldehydes,ketones, esters, phenols, acids, and aliphatic, aromatic and otheralcohols.

Preservatives also can be added to the compositions of the presentinvention to prevent bacterial growth. Suitable preservatives approvedfor use in oral compositions such as methylparaben, propylparaben andsodium benzoate can be added in safe and effective amounts.

Other ingredients can be used in the dentifrice composition, such asdesensitizing agents, healing agents, other caries preventative agents,chelating/sequestering agents, vitamins, amino acids, proteins, otheranti-plaque/anti-calculus agents, opacifiers, antibiotics, anti-enzymes,enzymes, pH control agents, oxidizing agents, antioxidants, and thelike.

EXAMPLES

The invention is further illustrated by the following examples, whichare not to be construed in any way as imposing limitations to the scopeof this invention. Various other aspects, modifications, and equivalentsthereof which, after reading the description herein, may suggestthemselves to one of ordinary skill in the art without departing fromthe spirit of the present invention or the scope of the appended claims.

The multipoint BET surface areas disclosed herein were determined on aMicromeritics TriStar II 3020 V1.03, using the BET nitrogen adsorptionmethod of Brunaur et al., J. Am. Chem. Soc., 60, 309 (1938).

Mercury total intruded volumes were measured on a Micromeritics AutoPoreIV 9520, previously calibrated with a silica-alumina reference materialavailable from Micromeritics. As generally known (see Halsey, G. D., J.Chem. Phys. (1948), 16, 931), the mercury porosimetry technique is basedon the intrusion of mercury into a porous structure under stringentlycontrolled pressures. From the pressure versus intrusion data, theinstrument generates volume and size distributions using the Washburnequation. Since mercury does not wet most substances and will notspontaneously penetrate pores by capillary action, it must be forcedinto the pores by the application of external pressure. The requiredpressure is inversely proportional to the size of the pores, and onlyslight pressure is required to intrude mercury into large macropores,whereas much greater pressures are required to force mercury intomicropores. Higher pressures are required to measure the pore sizes andsurface areas of the micropores present on the surfaces of silicaproducts disclosed herein.

The total intruded volume (HgI) was measured by mercury porosimetryusing a Micromeritics Autopore IV 9520. Samples were dried at 105° C.for two hours prior to analysis. The pore diameters were calculated bythe Washburn equation employing a contact angle Theta (θ) equal to 130°and a surface tension gamma equal to 484 dynes/cm. Mercury was forcedinto the voids of the material (both internal and intraparticleporosity) as a function of pressure, and the volume of the mercuryintruded per gram of sample was calculated at each pressure setting.Total mercury intrusion pore volume expressed herein represents thecumulative volume of mercury intruded at pressures from vacuum to 60,000psi. Increments in volume (cm³/g) at each pressure setting were plottedagainst the pore radius or diameter corresponding to the pressuresetting increments. The peak in the intruded volume versus pore radiusor diameter curve corresponds to the mode in the pore size distributionand identifies the most common pore size in the sample. Specifically,sample size was adjusted to achieve a stem volume of 30-50% in a powderpenetrometer with a 5 mL bulb and a stem volume of about 1.1 mL. Sampleswere evacuated to a pressure of 50 μm of Hg and held for 5 minutes.Mercury filled the pores from 4 to 60,000 psi with a 10 secondequilibrium time at each of approximately 150 data collection points.

CTAB surface areas disclosed herein were determined by absorption ofCTAB (cetyltrimethylammonium bromide) on the silica surface, the excessseparated by centrifugation and the quantity determined by titrationwith sodium lauryl sulfate using a surfactant electrode. Specifically,about 0.5 grams of the silica particles were placed in a 250-mL beakerwith 100 mL CTAB solution (5.5 g/L), mixed on an electric stir plate for1 hour, then centrifuged for 30 min at 10,000 RPM. One mL of 10% TritonX-100 was added to 5 mL of the clear supernatant in a 100-mL beaker. ThepH was adjusted to 3-3.5 with 0.1 N HCl and the specimen was titratedwith 0.01 M sodium lauryl sulfate using a surfactant electrode(Brinkmann SUR1501-DL) to determine the endpoint.

The median particle size (d50) refers to the particle size for which 50%of the sample has a smaller size and 50% of the sample has a largersize. Median particle size (d50), mean particle size (average), d90, andd10 were determined via the laser diffraction method using a Horiba LA300 instrument. Samples were de-agglomerated using ultrasonic vibrationfor 2 minutes.

For pour density and pack density, 20 grams of the sample were placedinto a 250 mL graduated cylinder with a flat rubber bottom. The initialvolume was recorded and used to calculate the pour density by dividingit into the weight of sample used. The cylinder was then placed onto atap density machine where it was rotated on a cam at 60 RPM. The cam isdesigned to raise and drop the cylinder a distance of 5.715 cm once persecond, until the sample volume is constant, typically for 15 min. Thisfinal volume was recorded and used to calculate the pack density bydividing it into the weight of sample used.

The Einlehner abrasion value is a measure of the hardness/abrasivenessof silica particles, and is described in detail in U.S. Pat. No.6,616,916, incorporated herein by reference, and involves an EinlehnerAT-1000 Abrader generally used as follows: (1) a Fourdrinier brass wirescreen is weighed and exposed to the action of a 10% aqueous silicasuspension for a fixed length of time; (2) the amount of abrasion isthen determined as milligrams of brass lost from the Fourdrinier wirescreen per 100,000 revolutions (mg lost/100,000 revolutions).

CPC compatibility (%) was determined as follows. 27 grams of a 0.3%solution of CPC (cetylpyridinium chloride) were added to a 3 g sample ofthe silica to be tested. The silica was previously dried at 105° C. to150° C. to a moisture content of 2% or less, and the pH of the samplewas measured to ensure the 5% pH was between 5.5 and 7.5. The mixturewas shaken for a period of 10 minutes. Accelerated aging testingrequires agitation of the test specimen for 1 week at 140° C. Afteragitation was complete, the sample was centrifuged and 5 mL of thesupernatant was passed through a 0.45 μm PTFE milli-pore filter anddiscarded. An additional 2 g of supernatant was then passed through thesame 0.45 μm PTFE milli-pore filter and then added to a vial containing38 g of distilled water. After mixing, an aliquot of the sample wasplaced in a cuvette (methyl methacrylate) and the U.V. absorbance wasmeasured at 268 nm. Water was used as a blank. The % CPC compatibilitywas determined by expressing as a percentage the absorbance of thesample to that of a CPC standard solution prepared by this procedurewith the exception that no silica was added.

Stannous compatibility (%) was determined as follows. A stock solutioncontaining 431.11 g of 70% sorbitol, 63.62 g of de-oxygenated deionizedwater, 2.27 g of stannous chloride dihydrate, and 3 g of sodiumgluconcate was prepared. 34 g of the stock solution was added to a 50 mLcentrifuge tube containing 6 g of the silica sample to be tested. Thecentrifuge tube was placed on a rotating wheel at 5 RPM and was aged for1 week at 40° C. After aging, the centrifuge tube was centrifuged at12,000 RPM for 10 minutes, and the stannous concentration in thesupernatant was determined by ICP-OES (inductively coupled plasmaoptical emission spectrometer). The stannous compatibility wasdetermined by expressing the stannous concentration of the sample as apercentage of the stannous concentration of a solution prepared by thesame procedure, but with no silica added.

Oil absorption values were determined in accordance with the rub-outmethod described in ASTM D281 using linseed oil (cc oil absorbed per 100g of the particles). Generally, a higher oil absorption level indicatesa particle with a higher level of large pore porosity, also described ashigher structure.

Water absorption values were determined with an Absorptometer “C” torquerheometer from C.W. Brabender Instruments, Inc. Approximately ⅓ of a cupof the silica sample was transferred to the mixing chamber of theAbsorptometer and mixed at 150 RPM. Water then was added at a rate of 6mL/min, and the torque required to mix the powder was recorded. As wateris absorbed by the powder, the torque will reach a maximum as the powdertransforms from free-flowing to a paste. The total volume of water addedwhen the maximum torque was reached was then standardized to thequantity of water that can be absorbed by 100 g of powder. Since thepowder was used on an as received basis (not previously dried), the freemoisture value of the powder was used to calculate a “moisture correctedwater AbC value” by the following equation.

${{Water}\mspace{14mu} {Absorption}} = \frac{{\text{water}\mspace{14mu} {absorbed}\mspace{14mu} ({cc})} + {\% \mspace{14mu} {moisture}}}{\left( {{100\mspace{14mu} (g)} - {\% \mspace{14mu} {moisture}}} \right)/100}$

The Absorptometer is commonly used to determine the oil number of carbonblack in compliance with ASTM D 2414 methods B and C and ASTM D 3493.

The pH values disclosed herein (5% pH) were determined in an aqueoussystem containing 5 wt. % solids in deionized water using a pH meter.

The 325 mesh residue (wt. %) of the silica sample was measured utilizinga U.S. Standard Sieve No. 325, with 44 micron or 0.0017 inch openings(stainless steel wire cloth), by weighing a 10.0 gram sample to thenearest 0.1 gram into the cup of a 1 quart Hamilton mixer (Model No.30), adding approximately 170 mL of distilled or deionized water, andstirring the slurry for at least 7 min. The mixture was transferred ontothe 325 mesh screen and water was sprayed directly onto the screen at apressure of 20 psig for two minutes, with the spray head held about fourto six inches from the screen. The remaining residue was thentransferred to a watch glass, dried in an oven at 150° C. for 15 min,then cooled, and weighed on an analytical balance.

Loss on drying (LOD) was performed by measuring the weight loss (wt. %)of a sample of the silica particles after drying at 105° C. for 2 hours.Loss on ignition (LOI) was performed by measuring the weight loss (wt.%) of a pre-dried sample (after drying at 105° C. for 2 hours) of thesilica particles after heating at 1000° C. for 1 hour (USP NF for SiO₂method).

The cleaning performance of the silica materials in a dentifricecomposition is typically quantified by a Pellicle Cleaning Ratio (“PCR”)value. The PCR test measures the ability of a dentifrice composition toremove pellicle film from a tooth under fixed brushing conditions. ThePCR test is described in “In Vitro Removal of Stain with Dentifrice” G.K. Stookey, et al., J. Dental Res., 61, 1236-9, 1982, which isincorporated herein by reference for its teaching of PCR. PCR values areunitless.

The Relative Dentin Abrasion (RDA) values of the dentifrice compositionsof the invention were determined according to the method set forth byHefferen, Journal of Dental Res., July-August 1976, 55 (4), pp. 563-573,and described in Wason U.S. Pat. Nos. 4,340,583, 4,420,312 and4,421,527, which are each incorporated herein by reference for theirteaching of RDA measurements. RDA values are unitless.

Examples 1a-6A Comparative Silica Particles and Spherical SilicaParticles

Example 1A was a conventional silica material commercially availablefrom Evonik Corporation, which has an irregular and non-sphericalparticle morphology.

For Examples 2A-6A, a continuous loop reactor process (see e.g., U.S.Pat. Nos. 8,945,517 and 8,609,068) was used to produce silica particles.FIG. 1 illustrates the continuous loop reactor apparatus, which wasconfigured in a recycle loop such that reaction slurry was circulatednumerous times before it was discharged. The loop was comprised ofsections of fixed pipe joined together by sections of flexible hose. Theinternal diameter of the piping/hose was approximately 1″. On one sideof the loop, a pump was placed to circulate the reaction slurry, and onthe opposite side a Silverson in-line mixer was installed to provideadditional shear to the system and also to feed the acid component. Inbetween the pumps, a static mixer heat exchanger was installed toprovide a means to control the temperature during production of thesilica material. The discharge pipe, located after the acid additionpoint, allowed the product to discharge as a function of the rates atwhich silicate and acid were added. The discharge pipe also was fittedwith a back pressure valve to enable the system to operate attemperatures greater than 100° C. The product discharge pipe wasoriented to collect product into a tank for additional modification(e.g., pH adjustment), or was discharged directly into a rotary or presstype filter. Optionally, acid could be added into the product dischargeline to avoid pH adjustment when the silica product was prepared at a pHgreater than 7.0.

For certain examples, the Silversion in-line mixer was modified toprovide a high level of mixing without providing shear. This wasaccomplished by removing the stator screen from the Silverson mixer andoperating the unit with only the backing plate and the normal mixerhead. Particle size thus could be controlled by changing the Silversonoutput rate and the recirculation rate (e.g., a reduction in both ratescan increase the average particle size).

Prior to the introduction of acid and silicate into the system forExamples 2A-6A, precipitated silica, sodium sulfate, sodium silicate andwater were added and recirculated at 80 L/min. This step was performedto fill the recycle loop with the approximate contents andconcentrations of a typical batch to minimize the purging time beforethe desired product could be collected.

For Example 2A, 1.5 kg of Example 1A, 1.34 kg of sodium sulfate, 11.1 Lof sodium silicate (3.32 MR, 19.5%) and 20 L of water were added to therecirculation loop, followed by heating to 95° C. with recirculation at80 L/min with the Silverson operating at 60 Hz (3485 RPM) with thenormal rotor/stator configuration. Sodium silicate (3.32 MR, 19.5%) andsulfuric acid (17.1%) were added simultaneously to the loop at asilicate rate of 1.7 L/min and an acid rate sufficient to maintain a pHof 7.5. If necessary, the acid rate was adjusted accordingly to maintainthe pH. Acid and silicate were added under these conditions for 40minutes to purge unwanted silica out of the system before the desiredmaterial was collected. After 40 minutes had passed, the collectionvessel was emptied and its contents discarded. The silica product wasthen collected in a vessel with stirring at 40 RPM while maintaining thetemperature at approximately 80° C. After the desired quantity ofproduct was collected, addition of acid and silicate were stopped andthe contents of the loop were allowed to circulate. The silica productin the collection vessel was adjusted to pH 6.0 with the manual additionof sulfuric acid and was then filtered, and washed to a conductivity of˜1500 μS. The pH of the slurry was then readjusted to pH 6.0 withsulfuric acid and spray dried.

For Example 3A, 1.5 kg of Example 1A, 1.34 kg of sodium sulfate, 11.1 Lof sodium silicate (2.65 MR, 26.6%) and 20 L of water were added to therecirculation loop, followed by heating to 95° C. with recirculation at80 L/min with the Silverson operating at 30 Hz (1742 RPM) with thestator screen removed. Sodium silicate (2.65 MR, 26.6%) and sulfuricacid (22.8%) were added simultaneously to the loop at a silicate rate of1.7 L/min and an acid rate sufficient to maintain a pH of 7.5. Ifnecessary, the acid rate was adjusted accordingly to maintain the pH.Acid and silicate were added under these conditions for 40 minutes topurge unwanted silica out of the system before the desired material wascollected. After 40 minutes had passed, the collection vessel wasemptied and its contents discarded. The silica product was thencollected in a vessel with stirring at 40 RPM while maintaining thetemperature at approximately 80° C. After the desired quantity ofproduct was collected (500 L), addition of acid and silicate werestopped and the contents of the loop were allowed to circulate.

Then, for surface area reduction, the silica product in the collectionvessel was transferred to a batch reactor and heated to 95° C. withstirring at 80 RPM and recirculation at 80 L/min Sodium silicate (2.65MR, 26.6%) was added to the reactor until a pH of 9.5 (+/−0.2) wasreached. Once the pH was reached, sodium silicate (2.65 MR, 26.6%) andsulfuric acid (22.8%) were added at rates of 1.66 L/min and 0.80 L/min,respectively. If needed, the acid rate was adjusted to maintain the pHof 9.5 (+/−0.2). After a total time of 60 minutes, the flow of sodiumsilicate was stopped and the pH was adjusted to 7.0 with continuedaddition of sulfuric acid (22.8%) at 0.80 L/min. The batch was digestedfor 15 minutes at pH 7.0, and then filtered and washed to a conductivityof <1500 μS. Prior to drying, the pH of the silica slurry was adjustedto 5.0 with sulfuric acid and spray dried to a target moisture of 5%.

For Example 4A, 1.5 kg of Example 1A, 1.34 kg of sodium sulfate, 11.1 Lof sodium silicate (3.3 MR, 19.5%) and 20 L of water were added to therecirculation loop, followed by heating to 90° C. with recirculation at60 L/min with the Silverson operating at 30 Hz (1742 RPM) with thestator screen removed. Sodium silicate (3.3 MR, 19.5%) and sulfuric acid(17.1%) were added simultaneously to the loop at a silicate rate of 1.7L/min and an acid rate sufficient to maintain a pH of 7.5. If necessary,the acid rate was adjusted accordingly to maintain the pH. Acid andsilicate were added under these conditions for 40 minutes to purgeunwanted silica out of the system before the desired material wascollected. After 40 minutes had passed, the collection vessel wasemptied and its contents discarded. The silica product was thencollected in a vessel with stirring at 40 RPM while maintaining thetemperature at approximately 80° C. After the desired quantity ofproduct was collected (700 L), addition of acid and silicate werestopped and the contents of the loop were allowed to circulate.

Then, for surface area reduction, the silica product in the collectionvessel was transferred to a batch reactor and heated to 95° C. withstirring at 80 RPM. Sodium silicate (3.3 MR, 19.5%) was added to thereactor until a pH of 9.5 (+/−0.2) was reached. Once the pH was reached,sodium silicate (3.32 MR, 19.5%) and sulfuric acid (17.1%) were added atrates of 2.4 L/min and 0.98 L/min, respectively. If needed, the acidrate was adjusted to maintain the pH of 9.5 (+/−0.2). After a total timeof 60 minutes, the flow of sodium silicate was stopped and the pH wasadjusted to 7.0 with continued addition of sulfuric acid (17.1%) at 0.81L/min. The batch was digested for 15 minutes at pH 7.0, and thenfiltered and washed to a conductivity of <1500 μS. Prior to drying, thepH of the silica slurry was adjusted to 5.0 with sulfuric acid and spraydried to a target moisture of 5%.

For Example 5A, 1.5 kg of Example 1A, 1.34 kg of sodium sulfate, 11.1 Lof sodium silicate (2.65 MR, 26.6%) and 20 L of water were added to therecirculation loop, followed by heating to 95° C. with recirculation at80 L/min with the Silverson operating at 30 Hz (1742 RPM) with thestator screen removed. Sodium silicate (2.65 MR, 26.6%) and sulfuricacid (22.8%) were added simultaneously to the loop at a silicate rate of1.7 L/min and an acid rate sufficient to maintain a pH of 7.5. Ifnecessary, the acid rate was adjusted accordingly to maintain the pH.Acid and silicate were added under these conditions for 40 minutes topurge unwanted silica out of the system before the desired material wascollected. After 40 minutes had passed, the collection vessel wasemptied and its contents discarded. The silica product was thencollected in a vessel with stirring at 40 RPM while maintaining thetemperature at approximately 80° C. After the desired quantity ofproduct was collected (500 L), addition of acid and silicate werestopped and the contents of the loop were allowed to circulate.

Then, for surface area reduction, the silica product in the collectionvessel was transferred to a batch reactor and was heated to 95° C. withstirring at 80 RPM and recirculation at 80 L/min Sodium silicate (2.65MR, 26.6%) was added to the reactor until a pH of 9.5 (+/−0.2) wasreached. Once the pH was reached, sodium silicate (2.65 MR, 26.6%) andsulfuric acid (22.8%) were added at rates of 1.66 L/min and 0.80 L/min,respectively. If needed, the acid rate was adjusted to maintain the pHof 9.5 (+/−0.2). After a total time of 60 minutes, the flow of sodiumsilicate was stopped and the pH was adjusted to 7.0 with continuedaddition of sulfuric acid (22.8%) at 0.80 L/min. The batch was digestedfor 15 minutes at pH 7.0, and then filtered and washed to a conductivityof <1500 μS. Prior to drying, the pH of the silica slurry was adjustedto 5.0 with sulfuric acid and spray dried to a target moisture of 5%.

For Comparative Example 6A, 1.5 kg of Example 1A, 1.34 kg of sodiumsulfate, 11.1 L of sodium silicate (3.32 MR, 13.0%) and 20 L of waterwere added to the recirculation loop, followed by heating to 65° C. withrecirculation at 80 L/min with the Silverson operating at 60 Hz (1742RPM) with the normal rotor/stator configuration. Sodium silicate (3.32MR, 13.0%) and sulfuric acid (11.4%) were added simultaneously to theloop at a silicate rate of 2.5 L/min and an acid rate sufficient tomaintain a pH of 7.4. If necessary, the acid rate was adjustedaccordingly to maintain the pH. Acid and silicate were added under theseconditions for 40 minutes to purge unwanted silica out of the systembefore the desired material was collected. After 40 minutes had passed,the collection vessel was emptied and its contents discarded. The silicaproduct was then collected in a vessel with stirring at 40 RPM whilemaintaining the temperature at approximately 80° C. After the desiredquantity of product was collected (500 L), addition of acid and silicatewere stopped and the contents of the loop were allowed to circulate.

Then, for surface area reduction, the silica product in the collectionvessel was transferred to a batch reactor and was heated to 95° C. withstirring at 80 RPM and recirculation at 80 L/min Sodium silicate (3.32MR, 13.0%) was added to the reactor until a pH of 9.5 (+/−0.2) wasreached. Once the pH was reached, sodium silicate (3.32 MR, 13.0%) andsulfuric acid (11.4%) were added at rates of 2.30 L/min and 0.83 L/min,respectively. If needed, the acid rate was adjusted to maintain the pHof 9.5 (+/−0.2). After a total time of 175 minutes, the flow of sodiumsilicate was stopped and the pH was adjusted to 7.0 with continuedaddition of sulfuric acid (11.4%) at 0.80 L/min. The batch was digestedfor 10 minutes at pH 7.0, and then filtered and washed to a conductivityof <1500 μS. Prior to drying, the pH of the silica slurry was adjustedto 5.0 with sulfuric acid and spray dried to a target moisture of 5%.

Table I summarizes certain properties of spherical silica particles3A-5A and comparative silica materials 1A-2A and 6A. As compared toExamples 1A-2A, the silica materials of Examples 3A-5A had excellentstannous compatibility and CPC compatibility, significantly lower BETsurface area, CTAB surface area, and pore volume, and higher pourdensity and pack density. Representative SEM images for Examples 2A-5Aare provided as FIGS. 2-5, respectively. Examination of the SEM imagesdemonstrated a narrow particle size distribution and spherical particlemorphology for the silica particles of Examples 3A-5A. The respectivesphericity factor (S₈₀) for each of Examples 3A-5A is greater than 0.9.

SEM images for the comparative silica of Example 6A are provided in FIG.6. While the silica product of Example 6A was generally spherical(sphericity is less than 0.9), it is not as spherical as the silicamaterials of Examples 3A-5A. Further, as compared to Example 6A, thelarger particle size silica materials of Examples 3A-5A hadsignificantly lower pore volume and higher pour density and pack density(see Table I).

Examples 1B-5B Example 5C Toothpaste Formulations and PCR and RDATesting

Samples of silicas 1A-5A were used in toothpaste formulations 1B-5B at a20 wt. % loading of the respective silica, and in toothpaste formulation5C at a 10 wt. % loading of the respective silica, as summarized inTable II. The toothpaste formulations were prepared using standardmethods known in the art using the components listed in Table II.

PCR and RDA testing (at the Indiana University School of Dentistry) wereconducted on the toothpaste formulations to determine the impact of thesilica properties on the PCR and RDA performance. Table III summarizesthe PCR and RDA data for the toothpaste formulations. Unexpectedly, asthe particle size of the highly spherical particles increased, the PCRand the RDA both decreased. These results are unexpected and contrary tothat typically observed with traditional precipitated silica materials(which are irregularly shaped, and not spherical). While not wishing tobe bound by theory, it is believed that since RDA testing is performedon an irregular surface comprised of dentin and hollow dentin tubulesthat are approximately 2-3 μm in size, that the spherical silicaparticles fall partway into the tubules, and then gouge the oppositewall as they are pushed out of the tubule by the toothbrush as they moveacross the dentin surface.

Examples 7A-11A Irregular Silica Particles

Table IV summarizes certain properties of comparative silica materials7A-11A, which have an irregular and non-spherical particle morphology.Example 7A was a conventional silica material commercially availablefrom Evonik Corporation, and Examples 8A-11A were produced by airmilling an unmilled sample of Example 7A to a d50 particle size of 3.5μm (Example 8A), 6.2 μm (Example 9A), 9.4 μm (Example 10A, broadparticle size distribution), and 9.3 μm (Example 11A, narrow particlesize distribution).

Examples 7B-11B Toothpaste Formulations and PCR and RDA Testing

Samples of silicas 7A-11A were used in toothpaste formulations 7B-11B ata 20 wt. % loading of the respective silica, using the same formulationsshown in Table II for Examples 1B-5B.

PCR and RDA testing (at the Indiana University School of Dentistry) wereconducted on the toothpaste formulations to determine the impact of thesilica properties on the PCR and RDA performance. Table V summarizes thePCR and RDA data for the toothpaste formulations. As shown in Table V,as the particle size of the silica increased from 3.5 μm to 9.5 μm,there was no change in either the RDA or the PCR values. Thus, forirregular and non-spherical silica particles, there is no correlationbetween particle size and RDA and no correlation between particle sizeand PCR.

Discussion of Examples

By comparing the data in Table III with that of Table V, the behavior ofthe spherical silica materials is fundamentally (and surprisingly)different from that of traditional dental silicas, which arenon-spherical and irregularly shaped. Particle size and particle sizedistribution can be used to control RDA and PCR with highly sphericalmaterials, whereas for traditional irregularly-shaped silicas, particlesize and particle size distribution have no significant effect.

While not wishing to be bound by the following theory, it is believedthat the spherical particles initially gouge into the substrate, beforethey begin rolling across the surface (initially there is a lot of wear,but as the particles begin to roll, the wear is essentially eliminated),whereas a traditional non-spherical and irregularly shaped product wouldscratch the entire way across the substrate.

As shown in Table III, the RDA values for spherical products withparticle sizes of greater than 8 μm are less than 190. It is postulatedthat since the dentin surface is essentially non-homogeneous, comprisedof both porous mineral and organic content, the spherical particlespartially enter tubules and scrape the opposite side as they exit. Withvery spherical particles, as the particle size is increased, the depththat they can enter a tubule is reduced. This reduction in penetrationin the tubule (and increase in particle size) is thought to be thedriving factor for reducing RDA. A model for the spherical particle (ata small particle size) interacting with a dentin tubule is illustratedin FIG. 7.

A simple analogy would be driving over a pothole with a car tire. If thepothole is large relative to the car tire, a large bump is felt as thecar passes over the pothole. As the pothole is decreased in size, theintensity of the bump that is felt decreases, until the pothole is smallenough that the car tire does not fall very far into the hole. If thepothole was a fixed size, the same effect would be observed as the tireson the car were increased in size. In like manner, a model of sphericalparticles of increasing particle size (4 μm, 5 μm, 6 μm, 10 μm)interacting with dentin tubules of approximately 2.5 μm in size in shownin FIG. 8. The penetration depth of the particles into the tubules isreduced as particle size increases.

Using geometric calculations, the depth of penetration for a sphericalparticle can be calculated based upon its diameter, as described by J.M. Fildes et al., Wear 274-275 (2012) 414-422, incorporated herein byreference in its entirety. As it pertains to silica particle sizes andthe 2.5 μm width dentin tubules relevant to RDA, a plot of the depth ofpenetration versus particle diameter for a sphere can be generated (seeFIG. 9). There is a reduction in the depth of penetration of highlyspherical particles of roughly 80% as the particle size increases from3.5 μm to 12 μm.

The force required for a circular wheel (analogous to a sphericalparticle) to pass over a step of different heights (analogous to a depthof penetration) also can be calculated using formulas in “Physics forScientists and Engineers” Eighth Edition (2010); Serway|Jewett,incorporated herein by reference in its entirety. Using the assumptionthat the spherical particle only contacts one part of the tubule as itpasses through (with the exception of when it is at the bottom, then thepoint of contact is a step), a rough estimate of the force required forthe particle to exit the tubule can be calculated. Because dentifricecompositions are loaded by weight and numerically there are more smallparticles than large particles, it is believed that the calculated forcein Newtons should be on a weight basis (per gram basis). FIG. 10graphically represents the decrease in force required for 1 gram ofspherical particles to exit a 2.5 μm tubule as a function of increasingparticle size. The force is reduced by over 50% as the particle sizeincreases from 6 μm to 12 μm.

In sum, the figures, tables, and discussion above demonstrate that thebehavior of the spherical silica materials is fundamentally (andunexpectedly) different from that of traditional dental silicas, whichare non-spherical and irregularly shaped, particularly as it pertains toRDA performance Particle size is a key factor to control RDA and PCRwith highly spherical materials, unlike traditional irregularly-shapedsilicas, where particle size has no significant effect.

Examples 3D-6D and 12D-13D Toothpaste Formulations and PCR and RDATesting

Samples of silicas 3A-6A and 12A-13A were used in tartar-controltoothpaste formulations 3D-6D and 12D-13D at a 22 wt. % loading of therespective silica, as summarized in Table VI. The toothpasteformulations were prepared using standard methods known in the art usingthe components listed in Table VI. Silicas 12A-13A were conventional(irregularly shaped) silicas available from Evonik Corporation, with anominal d50 particle size in the 8-10 μm range, a BET surface areagreater than 20 m²/g, and generally poor stannous compatibility (<50%).

PCR and RDA testing (at the Indiana University School of Dentistry) wereconducted on the toothpaste formulations to determine the impact of thesilica properties on the PCR and RDA performance. Table VI summarizesthe PCR and RDA data for the toothpaste formulations. Toothpasteformulations 3D-5D (containing 22 wt. % of the respective sphericalsilicas of Examples 3A-5A) had equivalent PCR values to those ofExamples 12D-13D; however, the RDA values for the spherical silicaformulations were approximately 10% lower than for formulations usingirregularly shaped silicas. This benefit is also demonstrated by thehigher PCR/RDA ratios for spherical silica Examples 3D-5D.

Toothpaste formulation 6D (containing comparative silica 6A) exhibited aPCR value approximately 10% greater than for Examples 3A-5A, but the RDAvalue for Example 6D was 260, which would not be acceptable for use dueto the RDA value being greater than the upper limit of 250. Example 6Ddemonstrates that properties of the silica (other than sphericity), asshown in Table I for silica 6A, can lead to unacceptable RDA properties.

TABLE I Examples 1A-6A Example 1A 2A 3A 4A 5A 6A Description ComparativeComparative Spherical Spherical Spherical Comparative Silica SilicaSilica Silica Silica Silica Einlehner (mg lost/100 k rev) 15.2 1.4 11.516.3 15.3 19.5 CPC Compatibility (%) 0 0 87 81 91 — StannousCompatibility (%) 24 13 89 93 86 — BET Surface Area (m²/g) 56 89 1 2 0.55 Total Hg Intruded Pore Volume (cc/g) 0.92 0.75 0.58 0.60 0.49 0.96CTAB Surface Area (m²/g) 63 56 1 1 1 0 Oil Absorption (cc/100 g) 53 6650 32 38 75 Water AbC (cc/100 g) 70 75 61 66 57 94 5% pH 7.4 7.2 7.6 7.57.9 7.6 Median Particle Size - d50 (μm) 9.7 3.5 9.1 11.8 13.9 6.3 MeanParticle Size (μm) 12.5 3.8 9.3 11.5 13.7 6.6 d10 (μm) 2.2 2.1 1.9 1.82.2 1.8 d90 (μm) 26.8 6.0 15.7 18.8 22.1 11.1 Ratio of (d90 − d10)/d502.5 1.1 1.5 1.4 1.4 1.5 325 Mesh Residue (wt. %) 1.12 0.01 0.26 0.200.03 0.09 LOD (wt. %) 5.0 4.3 5.8 5.3 6.1 5.0 LOI (wt. %) 4.1 3.8 3.24.5 4.0 3.8 Sodium Sulfate (%) 2.08 0.82 1.85 0.35 0.35 — Pour Density(lb/ft³) 26.0 30.2 44.6 49.9 53.8 29.2 Pack Density (lb/ft³) 45.0 46.862.4 62.4 65.0 49.2 Average silica addition rate (%/min) — — 0.44 0.420.44 0.44

TABLE II Examples 1B-5B and Example 5C - Toothpaste formulations usedfor PCR/RDA testing (all values in wt. %) Example 1B 2B 3B 4B 5B 5CGlycerin (99.7%) 11.000 11.000 11.000 11.000 11.000 11.000 Sorbitol(70.0%) 40.007 40.007 40.007 40.007 40.007 40.007 Deionized water QS QSQS QS QS QS PEG-12 3.000 3.000 3.000 3.000 3.000 3.000 Cekol 2000A 1.2001.200 1.200 1.200 1.200 1.200 Tetrasodium pyrophosphate 0.500 0.5000.500 0.500 0.500 0.500 Sodium saccharin 0.200 0.200 0.200 0.200 0.2000.200 Sodium fluoride 0.243 0.243 0.243 0.243 0.243 0.243 Zeodent ® 1651.500 1.500 1.500 1.500 1.500 5.000 Silica Example 1A 20 Example 2A 20Example 3A 20 Example 4A 20 Example 5A 20 Example 5A 10 Titanium dioxide0.500 0.500 0.500 0.500 0.500 0.500 Sodium lauryl sulfate 1.200 1.2001.200 1.200 1.200 1.200 Flavor 0.650 0.650 0.650 0.650 0.650 0.650 Total100 100 100 100 100 100

TABLE III Examples 1B-5B and Example 5C - PCR and RDA data Example 1B 2B3B 4B 5B 5C BET Surface 56 89 1 2 0.5 0.5 Area (m²/g) Median Particle9.7 3.5 9.1 11.8 13.9 13.9 Size (μm) Mean Particle 12.5 3.8 9.3 11.513.7 13.7 Size (μm) Example Silica 20 20 20 20 20 10 (wt. %) PCR 106 118103 96 96 86 RDA 180 270 182 169 168 140 Ratio of 0.59 0.43 0.56 0.570.57 0.61 PCR/RDA

TABLE IV Examples 7A-11A Example 7A 8A 9A 10A 11A Einlehner (mglost/100k rev) 15.2 11.0 15.8 16.5 16.4 BET Surface Area (m²/g) 56 47 4445 50 CTAB Surface Area (m²/g) 63 40 36 38 26 Oil Absorption (cc/100 g)53 62 50 53 58 Water AbC (cc/100 g) 70 75 68 68 71 5% pH 7.4 7.8 7.8 7.77.8 LOD (wt. %) 6.5 6.4 10.4 10.2 5.6 Median Particle Size (μm) 9.7 3.56.2 9.4 9.3 Mean Particle Size (μm) 12.5 3.8 7.6 12.5 10.1 Ratio of(d90-d10)/d50 3.2 — — — — 325 Mesh Residue (wt. %) 1.12 0.20 1.5 3.8 0.4Sodium Sulfate (%) 2.08 1.14 1.14 1.14 1.00 Pour Density (lb/ft³) 26.017.0 22.0 26.0 26.0 Pack Density (lb/ft³) 45.0 25.0 39.0 39.0 45.0

TABLE V Examples 7B-11B - PCR and RDA data Example 7B 8B 9B 10B 11BMedian Particle Size (μm) 9.7 3.5 6.2 9.4 9.3 Mean Particle Size (μm)12.5 3.8 7.6 12.5 10.1 Example Silica (wt. %) 20 20 20 20 20 PCR 102 108103 105 106 RDA 212 218 216 222 214

TABLE VI Examples 3D-6D and 12D-13D - Toothpaste formulations (allvalues in wt. %) and PCR and RDA data Example 3D 4D 5D 6D 12D 13DDescription Spherical Spherical Spherical Comparative ComparativeComparative Silica Silica Silica Silica Silica Silica Sorbitol solution(70%) 32.577 32.577 32.577 32.577 32.577 32.577 Sodium hydroxide (50%soln.) 1.740 1.740 1.740 1.740 1.740 1.740 Water QS QS QS QS QS QSSaccharin sodium 0.450 0.450 0.450 0.450 0.450 0.450 Xanthan gum 0.3000.300 0.300 0.300 0.300 0.300 Sodium fluoride 0.243 0.243 0.243 0.2430.243 0.243 Carboxymethylcellulose 1.050 1.050 1.050 1.050 1.050 1.050Sodium acid pyrophosphate 3.190 3.190 3.190 3.190 3.190 3.190 Carbomer0.300 0.300 0.300 0.300 0.300 0.300 Flavor 1.4 1.4 1.4 1.4 1.4 1.4Sodium lauryl sulfate (28% soln.) 6.000 6.000 6.000 6.000 6.000 6.000Mica titanium dioxide 0.400 0.400 0.400 0.400 0.400 0.400 Silica Example3A 22 Example 4A 22 Example 5A 22 Example 6A 22 Example 12A 22 Example13A 22 Total 100 100 100 100 100 100 PCR 101 103 96 114 104 103 RDA 202207 187 260 231 227 Ratio of PCR/RDA 0.50 0.50 0.51 0.44 0.45 0.45

The invention is described above with reference to numerous aspects andspecific examples. Many variations will suggest themselves to thoseskilled in the art in light of the above detailed description. All suchobvious variations are within the full intended scope of the appendedclaims. Other aspects of the invention can include, but are not limitedto, the following (aspects are described as “comprising” but,alternatively, can “consist essentially of” or “consist of”):

Aspect 1. Silica particles characterized by:

(i) a d50 median particle size in a range from about 8 to about 20 μm;

(ii) a sphericity factor (S₈₀) of greater than or equal to about 0.9;

(iii) a BET surface area in a range from about 0.1 to about 8 m²/g;

(iv) a total mercury intrusion pore volume in a range from about 0.35 toabout 1.1 cc/g; and

(v) a loss on ignition (LOI) in a range from about 3 to about 7 wt. %.

Aspect 2. The silica particles defined in aspect 1, wherein the silicaparticles are further characterized by any suitable BET surface area, ora BET surface area in any range disclosed herein, e.g., from about 0.1to about 6 m²/g, from about 0.5 to about 5 m²/g, or from about 0.5 toabout 2 m²/g.

Aspect 3. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable pack density, or a pack density in any range disclosed herein,e.g., from about 40 to about 75 lb/ft³, from about 58 to about 70lb/ft³, from about 61 to about 72 lb/ft³, or from about 62 to about 65lb/ft³.

Aspect 4. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable pour density, or a pour density in any range disclosed herein,e.g., from about 40 to about 65 lb/ft³, from about 42 to about 60lb/ft³, from about 43 to about 58 lb/ft³, or from about 44 to about 54lb/ft³.

Aspect 5. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable Einlehner abrasion value, or an Einlehner abrasion value in anyrange disclosed herein, e.g., from about 7 to about 25, from about 8 toabout 20, from about 10 to about 22, or from about 11 to about 17 mglost/100,000 revolutions.

Aspect 6. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable total mercury intrusion pore volume, or a total mercuryintrusion pore volume in any range disclosed herein, e.g., from about0.35 to about 1.1, from about 0.35 to about 0.7, from about 0.35 toabout 0.65, from about 0.4 to about 0.65 cc/g, or from about 0.49 toabout 0.6 cc/g.

Aspect 7. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable Stannous compatibility, or a Stannous compatibility in anyrange disclosed herein, e.g., from about 40 to about 99%, from about 80to about 99%, from about 75 to about 95%, from about 80 to about 95%, orfrom about 86 to about 93%.

Aspect 8. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable CPC compatibility, or a CPC compatibility in any rangedisclosed herein, e.g., from about 70 to about 99%, from about 75 toabout 95%, from about 40 to about 95%, from about 78 to about 95%, orfrom about 81 to about 91%.

Aspect 9. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable median particle size (d50) and/or mean particle size (average),or a median particle size (d50) and/or mean particle size (average) inany range disclosed herein, e.g., from about 8 to about 18 μm, fromabout 9 to about 16 μm, or from about 9 to about 14 μm.

Aspect 10. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable ratio of (d90-d10)/d50, or a ratio of (d90-d10)/d50 in anyrange disclosed herein, e.g., from about 1.1 to about 2.2, from about1.2 to about 2, or from about 1.3 to about 1.5.

Aspect 11. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable water absorption, or a water absorption in any range disclosedherein, e.g., from about 40 to about 75 cc/100 g, from about 42 to about75 cc/100 g, from about 50 to about 65 cc/100 g, or from about 57 toabout 66 cc/100 g.

Aspect 12. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable oil absorption, or an oil absorption in any range disclosedherein, e.g., from about 20 to about 75 cc/100 g, from about 25 to about60 cc/100 g, from about 25 to about 55 cc/100 g, or from about 32 toabout 50 cc/100 g.

Aspect 13. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable CTAB surface area, or a CTAB surface area in any rangedisclosed herein, e.g., from 0 to about 10 m²/g, from 0 to about 6 m²/g,from 0 to about 4 m²/g, or from 0 to about 2 m²/g.

Aspect 14. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable pH, or a pH in any range disclosed herein, e.g., from about 5.5to about 9, from about 6.2 to about 8.5, from about 6.8 to about 8.2, orfrom about 7.5 to about 7.9.

Aspect 15. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable 325 mesh residue, or a 325 mesh residue in any range disclosedherein, e.g., less than or equal to about 1.2 wt. %, less than or equalto about 0.6 wt. %, or less than or equal to about 0.3 wt. %.

Aspect 16. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable sphericity factor (S₈₀), or a sphericity factor (S₈₀) in anyrange disclosed herein, e.g., greater than or equal to about 0.91,greater than or equal to about 0.92, or greater than or equal to about0.94.

Aspect 17. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable RDA at 20 wt. % loading, or a RDA at 20 wt. % loading in anyrange disclosed herein, e.g., from about 120 to about 200, from about130 to about 180, or from about 168 to about 182.

Aspect 18. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable ratio of PCR/RDA, or a ratio of PCR/RDA in any range disclosedherein, e.g., from about 0.4:1 to about 0.8:1, from about 0.5:1 to about0.7:1, or from about 0.56:1 to about 0.57:1.

Aspect 19. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable loss on drying (LOD), or a LOD in any range disclosed herein,e.g., from about 1 to about 15 wt. %, from about 3 to about 12 wt. %,from about 4 to about 8 wt. %, or from about 5.3 to about 6.1 wt. %.

Aspect 20. The silica particles defined in any one of the precedingaspects, wherein the silica particles are further characterized by anysuitable loss on ignition (LOI), or a LOI in any range disclosed herein,e.g., from about 3 to about 6 wt. %, from about 3.2 to about 5.5 wt. %,or from about 3.2 to about 4.5 wt. %.

Aspect 21. The silica particles defined in any one of the precedingaspects, wherein the silica particles are amorphous, or the silicaparticles are synthetic, or the silica particles are both amorphous andsynthetic.

Aspect 22. The silica particles defined in any one of the precedingaspects, wherein the silica particles are precipitated silica particles.

Aspect 23. A process for producing silica particles, the processcomprising:

(a) continuously feeding a first mineral acid and a first alkali metalsilicate into a loop reaction zone comprising a stream of liquid medium,wherein at least a portion of the first mineral acid and the firstalkali metal silicate react to form a base silica product in the liquidmedium of the loop reaction zone;

(b) continuously recirculating the liquid medium through the loopreaction zone;

(c) continuously discharging from the loop reaction zone a portion ofthe liquid medium comprising the base silica product;

(d) adding a second mineral acid and a second alkali metal silicateunder surface area reduction conditions to a mixture of water and thebase silica product; and

(e) ceasing the addition of the second alkali metal silicate andcontinuing the addition of the second mineral acid to the mixture toadjust the pH of the mixture to within a range from about 5 to about 8.5to produce the silica particles.

Aspect 24. The process defined in aspect 23, wherein steps (a)-(c) areperformed simultaneously.

Aspect 25. The process defined in aspect 23 or 24, wherein the loopreaction zone comprises a continuous loop of one or more loop reactorpipes.

Aspect 26. The process defined in any one of aspects 23-25, wherein thefirst mineral acid and the first alkali metal silicate are fed into theloop reaction zone at different points along the loop reaction zone.

Aspect 27. The process defined in any one of aspects 23-26, wherein theportion of the liquid medium discharged from the loop reaction zone isdischarged in a volumetric rate proportional to the amount of the firstmineral acid and the first alkali metal silicate fed into the loopreaction zone.

Aspect 28. The process defined in any one of aspects 23-27, whereinsteps (a)-(c) are performed in a continuous single loop reactor.

Aspect 29. The process defined in any one of aspects 23-28, wherein theliquid medium is recirculated through the loop reaction zone at a ratein a range from about 15 L/min to about 150 L/min, from about 60 L/minto about 100 L/min, or from about 60 L/min to about 80 L/min.

Aspect 30. The process defined in any one of aspects 23-29, wherein theliquid medium is recirculated through the loop reaction zone at a rateranging from about 50 vol. % per minute (the recirculation rate, perminute, is one-half of the total volume of the liquid medium in the loopreaction zone) to about 1000 vol. % per minute (the recirculation rate,per minute, is ten times the total volume of the liquid medium in theloop reaction zone), or from about 75 vol. % per minute to about 500vol. % per minute.

Aspect 31. The process defined in any one of aspects 23-30, wherein theliquid medium is recirculated through the loop reaction zone at a pH ina range from about 2.5 to about 10, from about 6 to about 10, from about6.5 to about 8.5, or from about 7 to about 8.

Aspect 32. The process defined in any one of aspects 23-31, wherein thefirst mineral acid comprises sulfuric acid, hydrochloric acid, nitricacid, phosphoric acid, or a combination thereof, and the first alkalimetal silicate comprises sodium silicate.

Aspect 33. The process defined in any one of aspects 23-32, wherein all(or substantially all, such as greater than 95 wt. %) of the liquidmedium is recirculated in step (b).

Aspect 34. The process defined in any one of aspects 23-33, wherein apump is utilized to recirculate the liquid medium through the loopreaction zone.

Aspect 35. The process defined in any one of aspects 23-34, wherein step(b) is performed at low shear or no shear conditions, e.g., the loopreaction zone does not comprise a stator screen or the loop reactionzone comprises a stator screen with openings greater than 3 mm² in crosssectional area (or greater than 10 mm², greater than 50 mm², greaterthan 100 mm², greater than 500 mm², etc., in cross sectional area),and/or a shear frequency in the loop reaction zone is less than1,000,000 interactions/min (or less than 750,000 interactions/min, lessthan 500,000 interactions/min, less than 250,000 interactions/min,etc.).

Aspect 36. The process defined in any one of aspects 23-35, whereinsteps (d)-(e) are performed in a vessel separate from the loop reactionzone, such as a stirred batch reactor.

Aspect 37. The process defined in any one of aspects 23-36, wherein thesurface area reduction conditions comprises an addition rate of thesecond alkali metal silicate to the mixture of an average silicaaddition rate in a range from about 0.2 to about 0.8 wt. % (or fromabout 0.25 to about 0.7 wt. %, from about 0.3 to about 0.55 wt. %, orfrom about 0.42 to about 0.44 wt. %) per minute, and/or at a maximumsilica addition rate of less than about 1.9 wt. % (or less than about1.5 wt. %, or less than about 1 wt. %) per minute.

Aspect 38. The process defined in any one of aspects 23-37, wherein thesecond mineral acid comprises sulfuric acid, hydrochloric acid, nitricacid, phosphoric acid, or a combination thereof, and the second alkalimetal silicate comprises sodium silicate.

Aspect 39. The process defined in any one of aspects 23-38, wherein thesurface area reduction conditions of step (d) comprise a time period ina range from about 45 minutes to about 5 hours, or from about 1 hour toabout 4 hours.

Aspect 40. The process defined in any one of aspects 23-39, wherein thesurface area reduction conditions of step (d) comprise a pH in a rangefrom about 9.2 to about 10.2, from about 9.3 to about 10, or from about9.3 to about 9.7.

Aspect 41. The process defined in any one of aspects 23-40, wherein thesurface area reduction conditions of step (d) comprise a temperature ina range from about 90 to about 100° C., or from about 90 to about 95° C.

Aspect 42. The process defined in any one of aspects 23-41, wherein, instep (d), the second alkali metal silicate and the second mineral acidare added to the mixture in any order, e.g., simultaneously,sequentially, alternating, as well as combinations thereof.

Aspect 43. The process defined in any one of aspects 23-42, wherein, instep (e), the addition rate of the second mineral acid to the mixture isat an average rate of addition of no more than 75% greater (no more than50% greater, or no more than 10% greater) than the average rate ofaddition of the second mineral acid in step (d).

Aspect 44. The process defined in any one of aspects 23-43, furthercomprising a step of filtering after step (e) to isolate the silicaparticles.

Aspect 45. The process defined in any one of aspects 23-44, furthercomprising a step of washing the silica particles after step (e).

Aspect 46. The process defined in any one of aspects 23-45, furthercomprising a step of drying (e.g., spray drying) the silica particlesafter step (e).

Aspect 47. The process defined in any one of aspects 23-46, wherein thesilica particles produced are defined in any one of aspects 1-22.

Aspect 48. Silica particles produced by the process defined in any oneof aspects 23-46.

Aspect 49. Silica particles defined in any one of aspects 1-22 producedby the process defined in any one of aspects 23-46.

Aspect 50. A composition comprising the silica particles defined in anyone of aspects 1-22 or 48-49.

Aspect 51. A dentifrice composition comprising the silica particlesdefined in any one of aspects 1-22 or 48-49.

Aspect 52. A dentifrice composition comprising from about 0.5 to about50 wt. % of the silica particles defined in any one of aspects 1-22 or48-49.

Aspect 53. A dentifrice composition comprising from about 5 to about 35wt. % of the silica particles defined in any one of aspects 1-22 or48-49.

Aspect 54. The dentifrice composition defined in any one of aspects51-53, wherein the composition further comprises at least one of ahumectant, a solvent, a binder, a therapeutic agent, a chelating agent,a thickener other than the silica particles, a surfactant, an abrasiveother than the silica particles, a sweetening agent, a colorant, aflavoring agent, and a preservative, or any combination thereof.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm.”

Every document cited herein, including any cross referenced or relatedpatent or application and any patent application or patent to which thisapplication claims priority or benefit thereof, is hereby incorporatedherein by reference in its entirety unless expressly excluded orotherwise limited. The citation of any document is not an admission thatit is prior art with respect to any invention disclosed or claimedherein or that it alone, or in any combination with any other referenceor references, teaches, suggests or discloses any such invention.Further, to the extent that any meaning or definition of a term in thisdocument conflicts with any meaning or definition of the same term in adocument incorporated by reference, the meaning or definition assignedto that term in this document shall govern.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A dentifrice composition comprising: a) binder; b) surfactant; c) silica particles; wherein the silica particles comprise: (i) a d50 median particle size in a range from about 4 to about 25 μm; (ii) a BET surface area in a range from 0 to about 10 m²/g; and (iii) a total mercury intrusion pore volume in a range from about 0.2 to about 1.5 cc/g.
 2. The dentifrice composition of claim 1, wherein the d50 median particle size is in a range from about 6 to about 25 μm.
 3. The dentifrice composition of claim 1, wherein the d50 median particle size is in a range from about 8 to about 20 μm.
 4. The dentifrice composition of claim 1, wherein the silica particles have a sphericity factor (S₈₀) and the sphericity factor (S₈₀) is greater than or equal to about 0.9.
 5. The dentifrice composition of claim 4, wherein the sphericity factor (S₈₀) is greater than or equal to about 0.92.
 6. The dentifrice composition of claim 1, wherein the BET surface area is in a range from about 0.05 to about 8 m²/g.
 7. The dentifrice composition of claim 6, wherein the BET surface area is in a range from about 0.1 to about 5 m²/g.
 8. The dentifrice composition of claim 1, wherein the total mercury intrusion pore volume is in a range from about 0.35 to about 1.1 cc/g.
 9. The dentifrice composition of claim 8, wherein the total mercury intrusion pore volume is in a range from about 0.4 to about 0.65 cc/g.
 10. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a pack density in a range from about 40 to about 75 lb/ft³.
 11. The dentifrice composition of claim 10, wherein the silica particles are further characterized by a pack density in a range from about 61 to about 72 lb/ft³.
 12. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a pour density in a range from about 40 to about 65 lb/ft³.
 13. The dentifrice composition claim 12, wherein the silica particles are further characterized by a pour density in a range from about 42 to about 60 lb/ft³.
 14. The dentifrice composition of claim 1, wherein the silica particles are further characterized by an Einlehner abrasion value in a range from about 10 to about 25 mg lost/100,000 revolutions.
 15. The dentifrice composition of claim 14, wherein the silica particles are further characterized by an Einlehner abrasion value in a range from about 7 to about 25 mg lost/100,000 revolutions.
 16. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a Stannous compatibility in a range from about 40 to about 99%.
 17. The dentifrice composition of claim 16, wherein the silica particles are further characterized by a Stannous compatibility in a range from about 50 to about 99%.
 18. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a CPC compatibility in a range from about 55 to about 99%.
 19. The dentifrice composition of claim 18, wherein the silica particles are further characterized by a CPC compatibility in a range from about 40 to about 95%.
 20. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a ratio of (d90-d10)/d50 in a range from about 1.1 to about 2.2.
 21. The dentifrice composition of claim 20, wherein the silica particles are further characterized by a ratio of (d90-d10)/d50 in a range from about 1.2 to about
 2. 22. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a water absorption in a range from about 40 to about 75 cc/100 g.
 23. The dentifrice composition of claim 22, wherein the silica particles are further characterized by a water absorption in a range from about 42 to about 75 cc/100 g.
 24. The dentifrice composition of claim 23, wherein the silica particles are further characterized by an oil absorption in a range from about 20 to about 75 cc/100 g.
 25. The dentifrice composition of claim 24, wherein the silica particles are further characterized by an oil absorption in a range from about 25 to about 55 cc/100 g.
 26. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a CTAB surface area in a range from 0 to about 10 m²/g.
 27. The dentifrice composition of claim 26, wherein the silica particles are further characterized by a CTAB surface area in a range from 0 to about 4 m²/g.
 28. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a 325 mesh residue of less than or equal to about 1.2 wt. %.
 29. The dentifrice composition of claim 28, wherein the silica particles are further characterized by a 325 mesh residue of less than or equal to about 0.6 wt. %.
 30. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a RDA at 20 wt. % loading of less than about
 250. 31. The dentifrice composition of claim 30, wherein the silica particles are further characterized by a RDA at 20 wt. % loading in a range from about 80 to about
 200. 32. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a ratio of PCR/RDA, at 20 wt. % loading, in a range from about 0.4:1 to about 1.1:1.
 33. The dentifrice composition of claim 32, wherein the silica particles are further characterized by a ratio of PCR/RDA, at 20 wt. % loading, in a range from about 0.5:1 to about 0.7:1.
 34. The dentifrice composition of claim 1, wherein the silica particles are further characterized by a loss on drying (LOD) in a range from about 1 to about 10 wt. %.
 35. The dentifrice composition of claim 34, wherein the silica particles are further characterized by a loss on drying (LOD) in a range from about 1 to about 5 wt. %.
 36. The dentifrice composition of claim 35, wherein the silica particles are further characterized by a loss on ignition (LOI) in a range from about 3 to about 10 wt. %.
 37. The dentifrice composition of claim 36, wherein the silica particles are further characterized by a loss on ignition (LOI) in a range from about 3 to about 6 wt. %.
 38. The dentifrice composition of claim 1, wherein the silica particles are precipitated silica particles.
 39. The dentifrice composition of claim 1, wherein the silica particles are amorphous.
 40. The dentifrice composition of claim 1, wherein the composition further comprises at least one of a humectant, a solvent, a therapeutic agent, a chelating agent, a thickener other than the silica particles, an abrasive other than the silica particles, a sweetening agent, a colorant, a flavoring agent, and a preservative, or any combination thereof. 